Robotic lawn mowers are gaining popularity—more and more people are discovering the charm of not having to move their lawn manually or with a powered lawn mower. Moreover, the robotic lawn mowers are usually powered by electricity from the electric grid, meaning that pollutants from engine powered lawn mowers are avoided.
Usually, robotic lawn mower are chargeable electric devices comprising two individually powered drive wheels, a mowing means, sensors to detect a work space boundary and means for allowing the robotic lawn mower to find its way to the charger.
When in operation, a robotic lawn mower will run back and forth over the working area, which is delimited by a boundary wire buried shallowly near the working area, through which wire an electric current having a specific signature is fed. The electric current fed through the wire will create a magnetic field. The sensors of the robotic lawn mower will notify a controller of the robotic law mower when the robotic lawn mower approaches a boundary wire, and at a predetermined position of the robotic mower vis-à-vis the boundary wire, the robotic mower will back away slightly perform a predetermined turn and continue in the forward direction away from the boundary wire.
In most robotic mowers, the turn is effected by rotating the drive wheels of the robotic mower in opposite directions such that the robotic mower turns around a vertical axis extending through the robotic mower between the drive wheels. The other wheel pair is usually hinged in order to allow for it to move in any direction.
This way of turning the robotic mower away from the boundary wire is flawless if the boundary wire is placed on even ground, but it has turned out that there will be problems with the turn if the boundary wire is provided in a slope, since the wheel having the worst grip often slips, causing wear of the lawn and possible stuck of the robotic mower, such that it cannot continue cutting without being helped manually to another position.
It is the object of the present invention to solve, or at least mitigate, the problem of wheel slip during turn of the robotic mower.